No satisfactory animal model is presently available for amyotrophic lateral sclerosis. In vitro studies in the past have demonstrated a toxic effect of serum from ALS patients on tissue cultures of motor neurons. This present proposal is an attempt to induce disease of the motor neurons in vivo by chronic passive transfer of serum proteins obtained from patients with ALS. Mice will be injected repeatedly for at least two months. Clinical and electrophysiological studies will be done at regular intervals and postmortem pathological studies performed after two months, or when disease is apparent.